1. Field of the Invention
This invention relates to a continuous process for the manufacture of phthalocyanine pigment dispersions of primarily beta crystal structure and more particularly to a continuous process for the manufacture of phthalocyanine blue pigment in a binder containing an organic solvent. The phthalocyanine blue pigment dispersion may be used in paste printing inks and solvent-based inks and coatings.
2. Description of the Prior Art
The manufacture of phthalocyanine pigment crude usually results in the formation of a product containing impurities of relatively large crystal size, and has been referred to in the art as phthalo crude. This crude requires some form of particle size reduction and/or purification to be useful as a pigment having the tinctorial strength and intensity necessary for use in compositions such as printing inks and coatings.
Various methods have been proposed by the prior art to reduce the particle size and improve the purity of the phthalo crude.
The use of an aqueous medium for milling phthalo crude is disclosed in U.S. Pat. No. 2,999,862. U.S. Pat. No. 3,775,149 relates to the preparation of phthalocyanine pigments and is specifically concerned with the milling of phthalo crude in aqueous suspension, in the presence of a surfactant, to give a filterable paste of phthalocyanine which is predominantly of the beta-pigment form. This method, however, results in flocculated product where the pigment is purified when recovered as a presscake or in dry form. Thus, flocculation of the pigment has been a desirable feature according to these prior art processes and has provided a means for purifying the pigment. However, the resultant presscake or dry form of the pigment must then be redispersed for use in products such as inks, coatings and paints, etc.
In related co-pending U.S. application Ser. No. 033,362 filed Apr. 26, 1979, now U.S. Pat. No. 4,427,810 a continuous method of producing an aqueous phthalocyanine pigment dispersion is described in detail.
We have now found that beta-phthalocyanine pigment can be produced by a continuous method in a binder containing an organic solvent that can then be used directly in solvent-based products such as oil-based paste inks and organic coatings. The pigment dispersion in organic solvent according to the invention thus eliminates two steps in the use of phthalo blue pigment, i.e., filtering flocculated pigment and redispersion for an end use.